A test of the variability vs. specificity hypotheses in the retention of a motor skill.

The variability of practice hypothesis suggests that practicing with task variations enhances motor learning (Schmidt, 1975). However, in tasks with only a single criterion goal to be learned, the evidence that variable practice enhances retention of this criterion task compared to constant practice (i.e. practicing without task variations) is somewhat mixed. Here, we addressed this question using a registered report format. Participants (n = 80) learned a bimanual shuffleboard task where the goal was to slide a virtual puck toward a target, which required participants to release the puck at a specified speed. Two groups of participants were tested - the Constant group practiced with a specific criterion target location (which requires no variation in the puck speed), whereas the Variable group practiced the criterion target location along with 4 additional target locations. Pre-registered comparisons of retention after 24-h showed no evidence of significant differences between groups, with a Bayesian analysis showing support for the null hypothesis. Other exploratory analyses also showed no significant differences between groups. These results indicate that the variability of practice hypothesis may not be as universal as typically assumed but, more broadly, highlight the difficulty in using two-group experimental designs for hypothesis-testing in motor learning.